1. Field of the Invention
The present invention relates to a case locking structure for junction boxes used in automotive wire harness systems.
2. Description of the Prior Art
Junction boxes used to connect a single automotive wire harness to plural electrical systems components concentrate all connections in a single box to achieve greater economy and productivity in wiring operations. Various types of junction boxes have been developed as wire harnesses have become smaller and terminal connector density has increased inside the junction box.
The typical junction box is a square plastic box comprising an upper case 1 and a lower case 2. The lower case 2 is fit inside the upper case 1 with a locking claw 2b provided on the side wall 2a of the lower case 2 engaging, from the inside of the upper case 1, a locking hole or recess 1b provided in the side wall 1a of the upper case 1.
The locking hole 1b and locking claw 2b are provided at specific points in the side walls of the upper case 1 and lower case 2, respectively, and the upper and lower cases are locked together by locking the locking claws 2b in the locking holes 1b.
The problem with this typical construction is that the locking claw 2b engages the locking hole 1b by means of the locking claw 2b projecting horizontally from the side wall 2a of the lower case 2. The locking claw 2b therefore works effectively against vertical forces (indicated by arrow a in FIG. 8), but is easily disengaged by forces applied horizontally to the case (arrow b).
As a result, when a mounting stay 3 used to mount the junction box to the body is provided on one side wall 1a of the upper case 1, a force F created by vibrations from tightening the mounting stay 3 bolt and by loads after installation acts to open the side wall 1a to the outside in the horizontal direction. This force deforms the side wall 1a of the upper case 1, causing the locking holes 1b to separate from the locking claws 2b of the lower case 2, and thus unlocking the upper case 1 from the lower case 2.